The present invention generally relates to medical devices and, more particularly, to atherectomy catheter devices.
A variety of techniques and instruments have been developed to remove obstructive material in arteries or other body passageways or to repair the arteries or body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaques in a patient""s arteries. The buildup of fatty deposits (atheromas) in the intimal layer (under the endothelium of a patient""s blood vessels) characterizes atherosclerosis. Over time, what is initially deposited as relatively soft, cholesterol-rich atheromatous material often hardens into a calcified atherosclerotic plaque. The atheromas may be referred to as stenotic lesions or stenoses while the blocking material may be referred to as stenotic material. If left untreated, such stenoses can so sufficiently reduce perfusion that angina, hypertension, myocardial infarction, strokes and the like may result.
Several kinds of atherectomy devices have been developed for attempting to remove some or all of such stenotic material. In one type of device, such as that shown in U.S. Pat. No. 5,092,873 (Simpson), a cylindrical housing, carried at the distal end of a catheter, has a portion of its side-wall cut out to form a window into which the atherosclerotic plaque can protrude when the device is positioned next to the plaque. An atherectomy blade, disposed within the housing, is then advanced the length of the housing to lance the portion of the atherosclerotic plaque that extends into the housing cavity. While such devices provide for directional control in selection of tissue to be excised, the length of the portion excised at each pass of the atherectomy blade is necessarily limited to the length of the cavity in the device. The length and relative rigidity of the housing limits the maneuverability and therefore also limits the utility of the device in narrow and tortuous arteries such as coronary arteries. Such devices are also generally limited to lateral cutting relative to the longitudinal axis of the device.
Another approach, which solves some of the problems relating to removal of atherosclerotic plaque in narrow and tortuous passageways, involves the use of an abrading device carried at the distal end of a flexible drive shaft. Examples of such devices are illustrated in U.S. Pat. No. 4,990,134 (Auth) and U.S. Pat. No. 5,314,438 (Shturman). In the Auth device, abrasive material such as diamond grit (diamond particles or dust) is deposited on a rotating burr carried at the distal end of a flexible drive shaft. In the Shturman device, a thin layer of abrasive particles is bonded directly to the wire turns of an enlarged diameter segment of the drive shaft. The abrading device in such systems is rotated at speeds up to 200,000 rpm or more, which, depending on the diameter of the abrading device utilized, can provide surface speeds of the abrasive particles in the range of 40 ft/sec. According to Auth, at surface speeds below 40 ft/sec his abrasive burr will remove hardened atherosclerotic materials but will not damage normal elastic soft tissue of the vessel wall. See, e.g., U.S. Pat. No. 4,990,134 at col. 3, lines 20-23.
However, not all atherosclerotic plaques are hardened, calcified atherosclerotic plaques. Moreover, the mechanical properties of soft plaques are very often quite close to the mechanical properties of the soft tissue of the vessel wall. Thus, one cannot always rely entirely on the differential cutting properties of such abrasives to remove atherosclerotic material from an arterial wall, particularly where one is attempting to remove all or almost all of the atherosclerotic material.
Moreover, a majority of atherosclerotic lesions are asymmetrical (i.e., the atherosclerotic plaque is thicker on one side of the artery than on the other). As will be understood, the stenotic material will be entirely removed on the thinner side of an eccentric lesion before it will be removed on the thicker side of the lesion. Accordingly, during removal of the remaining thicker portion of the atherosclerotic plaque, the abrasive burr of the Auth device or the abrasive-coated enlarged diameter segment of the drive shaft of the Shturman device will necessarily engage healthy tissue on the side that has been cleared. Indeed, lateral pressure by such healthy tissue against the abrading device is inherently required to keep the abrading device in contact with the remaining stenotic tissue on the opposite wall of the passageway. For stenotic lesions that are entirely on one side of an artery (a relatively frequent condition), the healthy tissue across from the stenotic lesion will be exposed to and in contact with the abrading device for substantially the entire procedure. Moreover, pressure from that healthy tissue against the abrading device will be, in fact, the only pressure urging the abrading device against the atherosclerotic plaque. Under these conditions, a certain amount of damage to the healthy tissue is almost unavoidable, even though undesirable, and there is a clear risk of perforation or proliferative healing response. In some cases, the xe2x80x9chealthy tissuexe2x80x9d across from a stenotic lesion may be somewhat hardened by the interaction (i.e., it has diminished elasticity); under such circumstances, the differential cutting phenomenon described by Auth will also be diminished, resulting in a risk that this xe2x80x9chealthyxe2x80x9d tissue may also be removed, potentially causing perforation.
Thus, notwithstanding the foregoing and other efforts to design a rotational atherectomy device, there remains a need for such a device that can advance through soft atheromas while providing minimal risk to the surrounding vessel wall. Preferably, the device also minimizes the risk of dislodging emboli, and provides the clinician with real-time feedback concerning the progress of the procedure.
In accordance with one aspect of the present invention, a rotational medical device is provided having an elongate flexible tubular body. The tubular body has a proximal end and a distal end. A rotatable element extends substantially throughout the length of the tubular body. A rotatable cutter is connected to the distal end of the rotatable element. At the proximal end of the tubular body, a control may be provided, having an indicator that indicates resistance to rotation of either the cutter tip or the rotatable element. Preferably, the tubular body is provided with a vacuum coupling to permit aspiration of material dislodged by the cutter tip. An indicator may be provided to indicate obstruction of or undesirably high resistance to flow in the aspiration pathway.
In accordance with another aspect of the present invention, a method of removing material from a vessel is provided. The first step of the method is providing an elongate flexible tubular body attached to a control at its proximal end and having a rotatable cutter disposed at its distal end. The distal end of the elongate body is then advanced transluminally through the vessel to the material to be removed. The rotatable cutter is rotated, and portions of the material to be removed are drawn by application of a vacuum and/or operation of the cutter proximally past the rotatable cutter and into the tubular body. Feedback may be provided to the operator in response to changes in the aspiration flow, vacuum and/or load on the rotatable cutter.
In accordance with a further aspect of the present invention, a rotatable cutter for use in an elongate flexible tubular catheter is provided for removing material from a vessel. The cutter has a cutter shaft having a proximal end and a distal end and a longitudinal axis of rotation extending between the two ends. A generally helical thread is provided on at least a distal portion of the cutter shaft. Also, at least one radially outwardly extending shearing flange is provided on a proximal portion of the cutter shaft.
A rotational medical device having an elongate flexible tubular body, such as a catheter, is provided in accordance with another aspect of the present invention. The tubular body has a proximal end and a distal end. A rotatable element is contained within the flexible tubular body, either in sliding contact with or spaced radially inwardly from the tubular body. Preferably, an aspiration lumen is defined by the space between the interior surface of a wall of the tubular body and the exterior surface of the rotatable element. A rotatable cutter is connected to the rotatable element at the distal end of the tubular body. The present invention also provides a control at the proximal end of the tubular body. The tubular body has a first cross-sectional area and the aspiration lumen has a second cross-sectional area wherein the cross-sectional area of the aspiration lumen is at least about 30% and preferably is as much as 50% or more of the cross-sectional area of the tubular body. Preferably, a guidewire lumen extends throughout the length of the tubular body, or through at least a distal portion of the tubular body. The catheter may be used with either a conventional closed tip guidewire, or with a hollow guidewire having a distal opening thereon such as for infusion of therapeutic drugs, contrast media or other infusible material.
In accordance with yet another aspect of the present invention, a method of removing material from a patient is provided. An elongate flexible tubular body, having a proximal end and a distal end, is provided. A rotatable tip is disposed at the distal end of the tubular body and a control is attached to the proximal end of the tubular body. The distal end of the tubular body is advanced to the location of the material to be removed. The control is manipulated to activate an aspirating vacuum through the tubular body. Then the control is manipulated to commence a rotation of the cutter to remove the material from the patient.